<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <title>Responsive HTML images demo</title>
    <style>
      html {
        font-family: sans-serif;
        background-color: gray;
      }

      body {
        max-width: 1200px;
        margin: 0 auto;
        background-color: white;
      }

      header {
        background: url(header.jpg) no-repeat center;
        height: 200px;
      }

      section {
        padding: 20px;
      }

      p {
        line-height: 1.5;
      }

      img {
        display: block;
        margin: 0 auto;
        max-width: 100%;
      }
    </style>
  </head>
  <body>
    <header>

    </header>

    <main>
      <section>
        <h1>My website</h1>

        <img srcset="elva-fairy-480w.jpg 480w,
                     elva-fairy-800w.jpg 800w"
             sizes="(max-width: 600px) 480px,
                    800px"
             src="elva-fairy-800w.jpg" alt="Elva dressed as a fairy">
      </section>
    </main>
  </body>
</html>
